Heatable fluid line with a heating power which can be set

ABSTRACT

The present invention relates to a fluid line for conducting and heating a medium, having a heating line comprising a conduit and an electrical heating element which is assigned to the conduit. In this case, a particular heating power per unit length can be set, the heating element comprising at least three heating conductors which run along the conduit. The ends of the heating conductors are connected to one another and can be connected to a supply voltage in such a manner that a plurality of heating conductors are connected in series and/or in parallel such that, for a particular supply voltage, the heating power of the fluid line is determined by the total resistance of the heating conductors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to German Utility ModelApplication No. DE 20 2008 003 908.8, filed Mar. 19, 2008, the contentof which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a heatable fluid line having a heatingline comprising a conduit and an electrical heating element which isarranged, in particular, on the circumference of the conduit, aparticular heating power being able to be set.

BACKGROUND OF THE INVENTION

An example of a fluid line is disclosed in EP 1 764 541. In the case ofthis heatable fluid line, at least one electrical heating conductor andat least two electrical supply lines are arranged on the circumferenceof the conduit such that they run in the longitudinal direction of theconduit, the heating conductor being alternately electrically connectedto one of the two power supply lines, to be precise alternately to thepositive pole and negative pole of the supply voltage. In this case, theconnecting points are at equal distances behind one another, as seen inthe longitudinal direction of the conduit. The electrical heatingconductor is connected to the supply lines by means of soldering,welding or crimping, for example. As a result of this configuration, thefluid line has a constant heating power per unit length. This makes itpossible to prefabricate the fluid line in long lengths and to cut it toany desired length, each length of line which has been cut to lengthhaving the same heating power per unit length. However, this known fluidline has the disadvantage that relatively high material costs areproduced since, in addition to the electrical heating conductor orconductors, at least two supply lines have to be respectivelyconcomitantly provided. An increased outlay in terms of production alsoresults during production on account of the necessary alternatingconnecting points between the heating conductor and the supply lines.Each heatable fluid line which has been prefabricated in such a mannerhas a defined heating power per unit length. However, if differentheating powers per unit length are required for different applications,it is necessary to prefabricate different heatable fluid lines with therespectively required heating powers per unit length, with the resultthat it is necessary to stockpile or store the prefabricated fluidlines. This also results in increased production costs.

SUMMARY

The present invention is based on the object of avoiding the abovedisadvantages and providing a heatable fluid line in which the desiredheating power per unit length can be adapted to the respectiveapplication before the fluid line is installed, but it is still possibleto prefabricate the fluid lines in any desired length.

According to the invention, this object is achieved by virtue of thefact that the heating element comprises at least three heatingconductors which are electrically insulated from one another and runalong the longitudinal direction of the conduit, and the ends of theelectrical heating conductors are connected to one another and can beconnected to an electrical supply voltage in such a manner that aplurality of heating conductors are connected in series and/or inparallel such that, for a particular supply voltage, the heating powerof the fluid line is determined by the total electrical resistance ofthe electrical heating conductors. After the fluid line according to theinvention has been cut to length, the present invention makes itpossible for the available electrical heating conductors to be connectedin any desired manner such that a total electrical resistance which issuitable for the required heating power is set.

The present invention also relates to a heating line for use in a fluidline according to the invention. In the case of such a heating lineaccording to the invention, four metal wires, which are provided withelectrical insulation, are advantageously arranged as electrical heatingconductors on the circumference of the conduit in the longitudinaldirection. Arranging four electrical heating conductors on thecircumference of the conduit results in twenty six different possiblecircuits as a parallel and/or series connection of the individualelectrical heating conductors, with the result that twenty six differenttotal electrical resistance values can be set, as a result of whichthere is a wide range of variation in the heating power which can berespectively achieved. It is within the scope of the invention to alsoproduce the electrical heating conductors from bands with anelectrically conductive coating or to produce the heating conductorsusing individual electrically conductive layers which are in the form ofstrips and are applied to the conduit. The electrical heating conductorsmay also be integrated inside the wall of the conduit. The electricalheating conductors may also run inside the conduit, for example in theform of a twisted conductor bundle.

According to the invention, the wide range of variation in theadaptability of the fluid line according to the invention to a widevariety of heating powers is also improved by virtue of at least one ofthe heating conductors, preferably all of the heating conductors, havingan electrical resistance per unit length which differs from theelectrical resistance per unit length of the other heating conductors.The electrical resistance of the individual heating conductors per unitlength can be changed, on the one hand, by means of an appropriateselection of materials and/or by changing the conductor cross section.In the event of the individual electrical heating conductors havingdifferent resistances, it is expedient if corresponding color coding ofthe heating conductors is provided.

Further advantageous embodiments of the invention are contained in thesubclaims and are explained in more detail using the exemplaryembodiments which are illustrated in the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a fluid line according to theinvention,

FIG. 2 shows a basic illustration of another embodiment of a heatingline according to the invention for use in a fluid line as shown in FIG.1,

FIG. 3 shows a basic view of an alternative embodiment of a heating lineaccording to the invention for use in a fluid line as shown in FIG. 1,

FIG. 4 shows a calculation table for determining the total electricalresistance of a fluid line according to the invention having fourelectrical heating conductors per conduit.

In the different figures, the same parts are always provided with thesame reference symbols.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in FIG. 1, a heatable fluid line according to theinvention comprises a heating line 1 comprising a conduit 2, on thecircumference of which an electrical heating element, which comprisesfour individual electrical heating conductors 3, 4, 5, 6 in theexemplary embodiment illustrated, is arranged. In the exemplaryembodiment illustrated, the heating conductors 3, 4, 5, 6 are formedfrom individual electrical resistance wires. These individual resistancewires each have an electrical resistance R3, R4, R5, R6 which isdependent on the electrical resistivity of the wire material and on thediameter of the wire and on the total length of the resistance wirewound around the conduit 2. In the exemplary embodiment illustrated, theheating conductors 3, 4, 5, 6 are wound around the conduit 2 in the formof a spiral parallel to one another and with a constant pitch. Theindividual heating conductors 3, 4, 5, 6 can be wound around the conduit2 by machine, for example. This allows continuous winding. As alsoillustrated, the heating conductors 3, 4, 5, 6 may be surrounded by anexternal protective layer 7 and this external protective layer 7 may beproduced from a wound adhesive tape or from an extruded layer or from aplastic shrink tube. This external protective layer 7 forms externalprotection against damage and moisture. In addition, the fluid line 1according to the invention is preferably surrounded by an externalprotective sleeve 8 which is preferably formed by a corrugated pipe or aprotective tube. In the exemplary embodiment illustrated, the externalprotective sleeve 8 is illustrated in the form of a corrugated pipe. Acircumferential air gap is preferably present between the externalprotective sleeve 8 and the protective layer 7.

The electrical heating conductors 3, 4, 5, 6 are preferably composed ofmetal but may likewise be produced from carbon material.

FIG. 2 illustrates another embodiment of a heating line according to theinvention. In this embodiment, the electrical heating conductors 3, 4,5, 6 are arranged on the circumference of the conduit 2 such that theyrun in the longitudinal direction of the conduit 2 and parallel to thelongitudinal axis of the latter. For the rest, the structure of thefluid line according to the invention with the heating line 1illustrated in FIG. 2 corresponds to that shown in FIG. 1.

FIG. 3 shows an alternative embodiment with regard to the arrangementof, for example, three heating conductors 3, 4, 5 on the circumferenceof the conduit 2 for the purpose of forming a heating line 1. In thiscase, the heating conductors 3, 4, 5 run in meandering fashion on thecircumference of the conduit 2 in the longitudinal direction of thelatter.

In the exemplary embodiments illustrated, three or four heatingconductors 3, 4, 5, 6 are respectively arranged on the circumference ofthe conduit 2. However, it is also within the scope of the invention toarrange a larger number of heating conductors on the circumference ofthe conduit 2. The heating conductors may have the same electricalresistance or else have a respectively different electrical resistance.As already stated, the electrical resistance of the heating conductorsis determined, on the one hand, by the selection of materials and, onthe other hand, by the length and cross section of the individualheating conductors. If the individual heating conductors have adifferent electrical resistance, it is expedient if the individualheating conductors have corresponding color coding such that a visualcheck is possible and it is possible to discern which of the individualheating conductors have the same electrical resistance or a differentelectrical resistance.

The inventive design of the heating line 1 or fluid line enablescontinuous manufacture, with the result that cost-effective productionand storage is possible.

So that a fluid flowing through the conduit 2 when in use is heated witha desired heating power, it is necessary for the fluid line according tothe invention to be able to generate a particular heating power. Thisheating power is dependent on the available supply voltage which, forexample in a motor vehicle, comprises a vehicle electrical systemvoltage of 12 volts DC. This heating power is also dependent on theelectrical resistance of the individual heating conductors and the totalelectrical resistance of the heating conductors. Depending on the mediumto be respectively heated, it is necessary for a particular heatingpower to always be able to be generated per unit length of the fluidline according to the invention. For this purpose, the invention nowprovides for the ends of the individual heating conductors 3, 4, 5, 6 tobe connected to one another and to the supply voltage in such a mannerthat the individual heating conductors are connected in series and/or inparallel such that, for the predefined supply voltage, the heating powerof the fluid line is determined by the total electrical resistance ofall heating conductors.

FIG. 4 uses a table to illustrate, for example, how resistance cascadingis possible, in the case of a four-conductor concept, that is to say thepresence of four heating conductors 3, 4, 5, 6 which are wound aroundthe conduit 2 in the form of a spiral with a constant pitch, byconnecting the individual heating conductors 3, 4, 5, 6 in paralleland/or in series. In this exemplary embodiment, the heating conductor 3has a resistance R3 of 20 ohms, the heating conductor 4 has a resistanceR4 of 13 ohms, the heating conductor 5 has a resistance R5 of 10 ohmsand the heating conductor 6 has a resistance R6 of 3 ohms. The pitch ofthe spiral winding of the individual heating conductors 3, 4, 5, 6 is30°, from which a length factor per m of 1.178 is calculated. Theresistance R3, R4, R5, R6 per m of the individual heating conductors 3,4, 5, 6, which is dictated by the material and diameter, is 16.978 ohmsin the heating conductor 3, 11.036 ohms in the heating conductor 4,8.489 ohms in the heating conductor 5 and 2.547 ohms in the heatingconductor 6. The table illustrates the individual possible ways ofconnecting the individual heating conductors 3, 4, 5, 6, p being used toindicate a parallel connection of the heating conductors 3, 4, 5, 6and + being used to indicate a series connection of the individualheating conductors 3, 4, 5, 6. A combination p1-p1 or p2-p2 indicateswhich resistances are connected in parallel with one another. As emergesfrom the table, twenty six different combinations are possible, with theresult that twenty six different total resistances can be set byconnecting the individual heating conductors 3, 4, 5, 6 of the heatingconductors 3, 4, 5, 6 in parallel and/or in series. In this case,provision is likewise made for individual heating conductors of theheating conductors 3, 4, 5, 6 not to be connected to the supply voltageat all, which is expressed in the illustrated table by no entry in theassociated field. The smallest resistance value of the overall circuitresults when the heating conductors 3, 4, 5 are connected in parallelwith one another and the heating conductor 6 is connected in series withthis parallel connection of the three heating conductors, and thehighest resistance of the heating conductors 3, 4, 5, 6 results when allheating conductors are connected in series with one another. The end ofthe series and/or parallel circuit comprising the individual heatingconductors 3, 4, 5, 6 is respectively connected to the supply voltage bymeans of appropriate connecting lines. In this respect, it may likewisebe expedient if, in addition to the heating conductors 3, 4, 5, 6, atleast one electrical connecting line for the voltage supply is providedin the fluid line according to the invention such that it runs along thepipeline 2. This electrical connecting line is surrounded by electricalinsulation.

According to the invention, it is thus possible to prefabricate a fluidline according to the invention which is provided with standardizedwinding of individual heating conductors 3, 4, 5, 6, and it is possibleto set the necessary heating power on the basis of the desired length ofthe fluid line by means of appropriate instructions for connecting theindividual heating conductors 3, 4, 5, 6. The same heating power canalso always be set in this manner for each unit length which has beencut to length.

The present invention is not restricted to the exemplary embodimentsillustrated and described but rather also comprises all embodimentswhich have the same effect in the sense of the invention. Furthermore,the invention has hitherto not yet been restricted to the combination offeatures defined in the respective independent claim either but rathermay also be defined by any other desired combination of particularfeatures of all the individual features disclosed as a whole. This meansthat, in principle, virtually any individual feature of the respectiveindependent claim may be omitted or may be replaced with at least oneindividual feature disclosed at another point in the application. Inthis respect, the claims should be understood as merely a first attemptat formulating an invention.

1. A fluid line for conducting and heating a medium, having a heatingline comprising a conduit and an electrical heating element which isassigned to the conduit, a particular heating power per unit lengthbeing able to be set, wherein the heating element comprises at leastthree heating conductors which run along the conduit, and the ends ofthe heating conductors are connected to one another and can be connectedto a supply voltage in such a manner that a plurality of heatingconductors are connected in series, connected in parallel, or acombination of being connected in parallel and in series, such that, fora particular supply voltage, the heating power of the fluid line isdetermined by the total resistance of the heating conductors.
 2. Thefluid line according to claim 1, wherein the heating conductors compriseindividual metal wires which are provided with electrical insulation. 3.The fluid line according to claim 1, wherein the electrical heatingconductors comprise individual bands with an electrically conductivecoating.
 4. The fluid line according to claim 1, wherein the electricalheating conductors comprise electrically conductive layers, which areapplied to the conduit.
 5. The fluid line according to claim 1, whereinthe electrical heating conductors are integrated inside the wall of theconduit.
 6. The fluid line according to claim 2, wherein the heatingconductors run inside the conduit.
 7. The fluid line according to claim2, wherein at least one of the heating conductors has an electricalresistance which differs from the electrical resistance of the otherheating conductors.
 8. The fluid line according to claim 2, whereinthere are four heating conductors.
 9. The fluid line according to claim8, wherein the heating conductors all have a different electricalresistance.
 10. The fluid line according to claim 7, wherein thedifferent electrical resistance of the heating conductors results from adifferent cross-sectional size of the heating conductors.
 11. The fluidline according to claim 7, wherein the heating conductors with differentresistances are each identified using a different color.
 12. The fluidline according to claim 1, wherein the heating conductors run around theconduit in the form of a spiral.
 13. The fluid line according to claim1, wherein the heating conductors run parallel to the longitudinal axisof the conduit.
 14. The fluid line according to claim 1, wherein theheating conductors run on the conduit in meandering fashion.
 15. Thefluid line according to claim 2, wherein the heating conductors run inone layer beside one another or in a plurality of layers above oneanother.
 16. The fluid line according to claim 2, wherein, in additionto the heating conductors, at least one electrical connecting line forthe voltage supply runs in the longitudinal direction of the conduit.17. The fluid line according to claim 2, wherein the conduit with theheating conductors is surrounded by an external protective layer. 18.The fluid line according to claim 2, wherein the conduit with theheating conductors is surrounded by an external protective sleeve. 19.The fluid line according to claim 2, wherein the heating conductorscomprise resistance conductors.
 20. The fluid line according to claim 4,wherein the conductive layers are in the form of strips.
 21. The fluidline according to claim 12, wherein the heating conductors run aroundthe conduit with the same pitch.
 22. The fluid line according to claim18, wherein the external protective sleeve comprises a corrugated pipe.